I use Easiteach as a teacher on a daily basic. I am also a teacher trainer for teaching with software at my school. Regarding features I don't hesitate to recommend Easiteach as a cheap alternative to Smart Notebook or Promethean Inspire but without limitations to any hardware brand. Easiteach has a much less used community platform (http://www.easilearn.com) than Smart, but loaded a lot of readymade content for free on it.
A comparison of features is available here:
http://www.teachertechnologies.com/comparing-smart-promethean-and-easiteachs-software-the-table/
This comparison doesn't include latest improvements in Easiteach NG, like the possibility to import Smart Notebook files.
However, interface and usability is unusual. Teachers who are already trained to work with Smart Notebook might need extra training to understand the concept of Easiteach. Once this is done, you can do great things with Easiteach. Regarding Easiteachs Glasmodus-Tool (a tool to write on any screen, similar to Smart Notebook 10) I recommend to use Chalkbox instead, which is a freeware alternative working with any touchable device and is much more convenient to use (http://www.habilience.com/product_chalkbox/).
With Windows 8 and multitouch we have two issues currently:
- A single touch is often interpreted as a double touch, which makes it a little inconvenient (but not impossible) to select objects. This bug doesn't appear with single touch boards or older versions of Windows. This bug is reported and will hopefully be solved with the next version of Easiteach.
- Easiteach doesn't have an option to lock an object in a way to move it in any direction on the one hand but without allowing to change its size on the other hand. This didn't matter in the past, since changing size wasn't possible in presentation mode and only here it would be necessary to lock size changing. However, in newer versions of Easiteach you can change size using multitouch gestures - which is a bug or inconsistent with Easiteachs general idea what the presentation modus is about. This bug is reported too.
Regarding costs I will write under localzuks comment from today.